Norwegian HPSG grammar NorSource

NorSource (Norwegian HPSG resource grammar) is a development of the Digital Linguistics Research Group at the Norwegian University of Science and Technology (NTNU),Trondheim. The application is licensed under the Lesser General Public License For Linguistic Resources.

Contents

Short history of the grammar

NorSource is a computational grammar of Norwegian, developed through the last 12 years. It has as its formal and theoretical framework Head-Driven Phrase Structure Grammar (HPSG) (Pollard and Sag 1994, Sag et al. 2003), and started as a computational project through the LinGO initiative at CSLI, Stanford, using the LKB platform (Copestake 2002), which is a general platform with the format of typed feature-structures (TFS), and has integrated in it a format of semantic representation called Minimal Recursion Semantics (‘MRS’; cf. Copestake et al. 2005). Before year 2000 there were three grammars in this framework, viz. the English Resource Grammar ('ERG'), the Japanese grammar 'Jacy', and the German grammar 'GG'. Essential to the development of further grammars of this type was the HPSG Grammar Matrix (‘the Matrix’; see Bender et al. 2002, 2010), which was mainly based on ERG, and had its first phase of deployment during the EU-project DeepThought (2002-4).

We can distinguish four main phases in the development of NorSource, with some of the key persons involved:

Phase 1 resided in the building of a basic core grammar around the Matrix skeleton (using the Matrix versions 0.1 – 0.6, as they developed; this included the MRS system). This stage included the accommodation of a 80,000 entries lexicon imported from the previously established resources TROLL and NorKompLex, where a verb valence code and a code for inflectional paradigms constituted major parts.

Phase 2 resided in the development of a fine-grained ontology and computing system of spatial and temporal relations, amenable to grammatical systems across languages and typologies, and a detailed semantics of comparative constructions. The grammar was also used as a part of a small Norwegian-Japanese MT system. In this period, the inflectional system was thoroughly revised. Main publications from this period are: Hellan and Beermann (2004), Bermann et al. (2004), Beermann and Hellan (2005).

Phase 3 was devoted to a thorough revision of the valence code, to accommodate a cross-linguistically defined classification system of valence and construction types. Main publications from this period are: Hellan (2008), Hellan and Dakubu (2009, 2010)

Phase 4 has been devoted to the use of the grammar in ‘external’ applications, see below, and in this connection involved updating the soft- and hardware basis of the grammar (in particular with ACE), and the construction of a server carrying web-facilities for the grammar itself, as well as the applications and resources just mentioned. There has been a general regimentation of the grammar code, and adaptation of the semantic system – MRS – according to the UTool restrictor on MRS objects, enabling the Reasoner mentioned shortly below. (See Bruland 2013)

‘External’ applications:

A. A ‘Grammar Sparrer’, as described in Hellan et al. 2013, accessed at A Norwegian Grammar Sparrer. This is a construct along the lines of Bender et al. 2004, and Suppes et al. 2014, falling within the overall initiatives described in Heift and Schultze 2007, where specific types of grammatical mistakes are accommodated by ‘mal-rules’ in an extended ‘mal’-version of the grammar, and parses involving such mal-phenomena are reported to the user as tutoring instructions. This system has been running as a webdemo since 2011.

B. A Multilingual Valence repository, based on NorSource and three further LKB grammars: The Spanish Resource Grammar, the Bulgarian grammar BURGER, and a grammar of Ga. Information from these grammars is imported in a uniform format into the repository. In essence, the valence code used in verbal lexical types (cf. 3.2 below) is expanded to alternative and more easily inspectable formats, and the verb lexicons of the languages involved are imported into a database organized according to the newer codes, and searchable in terms of these codes. See web access at Multilingual Verb Valence Lexicon, and for description, Hellan and Bruland 2013, and Hellan et al. 2014.

C. An initial version of a POS-tagger of Norwegian, reflecting the lexical inventory of the grammar, which amounts to appx. 85000 lexical entries, and a large number of proper names of various categories. The tagger currently offers all available POS-alternatives for a given word. See web access at http://regdili.hf.ntnu.no:8081/webtagger/tagger.

D. A simple Reasoner over movement and spatial information exported from the MRS. (See Bruland 2013.)

F. Aligned with the latter point, exploring ways of simplifying the grammar definition code, which in its Matrix shape is a remnant from a far more complex AVM notation system (from Pollard and Sag 1994) than is currently motivated. (See Hellan, forthcoming)

Point F is developed along a scheme of building small grammars for the exploration of specific features or alternative designs. A full computational grammar as such is a very ‘stiff’ construct where hardly any change can be made without many repercussions elsewhere in the structure, hence no major change is advisable unless it has been explored in a smaller format.

Some remarks on purposes and adequacy of the grammar

As a grammar of Norwegian, Norsource's first and foremost purpose is of course coverage in the sense in which a descriptively adequate Generative Grammar is supposed to attain coverage, namely through recursive enumeration of all and only the strings that count as grammatical in the language, and assigning each string so recognized a morpho-syntactic and semantic analysis. Correctness of analysis is decided on empirical grounds, using standard linguistic criteria of adequacy.

As a computational system, a further desideratum is that the grammar can serve as a component in one or more natural language processing applications, like those mentioned above. From the viewpoint of general linguistics, this concern has the proviso that for a grammar as a ‘generic’ device, its success in the usage domain should in principle be measured by how well it can go into a multitude of applications, not just a single one; this is also the ambition for the present grammar. In this respect the grammar is like a Fregean ‘Sinn’, in acting as a function from domains-of-use to deployable systems.

Moreover, the grammar has been developed with a view to the following overall desiderata:

Cross-grammar Generality

The content of the grammar should to as large an extent as possible be phrased in terms used or alignable with terms used in other grammars and for other languages, thereby enabling linguistic comparison using these grammars.

Interoperability

The grammar should attain as much interoperability with other applications as possible, manifested both on an ‘outer’ level enabling data flow and easy access, and on an ‘inner’ level ensuring information exchange from one system component to another. Thus, the grammar's files and productions (parses, etc.) should be transportable to other applications, and the codes in which its files are written should be readable by other applications, or able to be mapped into other codes.

Sustainability

The grammar should be in such a format, and be situated in such an over-all environment, that as much as possible of its capacity can be retained, independently of particular persons maintaining it or particular physical environments.

Adequacy of the grammar

The grammar must cover not only ‘core grammar’, but the whole array of constructs that can be used in texts of the language: ‘fragments’, abbreviations, interjections, and much more. It at the same time must attain ‘analytic depth’, which will include at least the following factors of morpho-syntactic structure and parameters of functional and semantic analysis (in addition comes a lexicon of significant size):

- syntactic argument structure (or valence: whether there is a subject, an object,
a second/indirect object, etc., referred to as grammatical functions);
- semantic argument structure, that is, how many participants are present in the situation depicted,
and possibly also which roles they play (such as ‘agent’, ‘patient’, etc.);
- linkage between syntactic and semantic argument structure, i.e., which grammatical functions
express which roles; - identity relations, part-whole relations, etc., between arguments;
- aspect and Aktionsart, that is, properties of the situation expressed by a sentence in terms of
whether it is dynamic/stative, continuous/instantaneous, completed/ongoing, etc..

If these, and other, factors can be addressed in a notional and formal system so cross-linguistically articulated that a grammar of a language L1, through its formal encoding, exposes values relative to the above parameters within a matrix of corresponding values for languages L2, L3, …, etc., then one is on the track of attaining the desideratum of cross-grammar generality. To a certain extent, the multilingual valence base mentioned above under phase 4, point A, is an illustration of this point.

Evaluation

A standard requirement on NLP applications is that they be amenable to evaluation. However, there exist so far few criteria for measuring how well a grammar as a whole performs with regard to 'analytic depth' or the other desiderata mentioned. The closest a grammar can come currently to being transparent for its adequacy is through certains types of 'self-declaration', of which we mention two:

- Test suites categorized for what analytic properties their parses should exhibit;
- Grammar internal categorization systems which carry agreed-upon general definitions,
the grammar thereby signaling that the constructs categorized have been designed
with the agreed-upon contents.

Both strategies are followed in the present grammar. The Test suites shown below reflect the performance of the grammar for the phenomena contained in the various suites, and in the grammar internal classification, the encoding of verb types is defined following the system laid out in Verbconstructions cross-linguistically - Introduction.